Spectrophotometer systems enable investigation of sample systems with multiple wavelengths of electromagnetic radiation. Ellipsometer, polarimeter or the like systems also enable investigation of sample systems with multiple wavelengths of electromagnetic radiation, but in adition provide insight to phase shifts entered between orthogonal components of a polarized beam of electromagnetic raditaion by interaction with a sample.
Two basically distinguishable Spectrophotometer system configurations are possible. The first comprises a spectroscopic source of electromagnetic radiation and a single detector which, in use, are applied sequentially to provide base-line and sample data at different times. The second configuration again comprises a spectroscopic source of electromagnetic radiation, but further provides a beam-splitter means to provide two beams of electromagnetic radiation, which two beams are simultaneoulsy applied to provide base-line and sample data, said base-line and sample data generation being mediated via two separate detectors. In either case said systems can include a monochrometer to allow selecting or scanning through wavelengths, or can provide multi-element detector(s) which simultaneously monitors a plurality of wavelengths.
Continuing, conventional dual, (in space), electromagnetic beam Spectrophotometer systems allow simultaneous monitoring of baseline reference, and sample system investigation intensities via different beams of electromagnetic radiation, hence, allow immediate comparison of sample to baseline data on a wavelength by wavelength basis. It is noted that the two beams are generally derived from a single spectroscopic source of electromagnetic radiation and are produced by a beam-splitter means. The simultaneous availability of baseline and sample system data enables forming the desired result of an output ratio of the sample system investigation intensity signal with the corresponding baseline reference intensity signal. Said methodology can be practiced whether data is sequentially acquired by a scan of wavelengths or a multiplicity of wavelengths is simultaneously investigated depending on, for instance, if a monochrometer and single detector, or wavelength separating means, (eg. dispersive element or a plurality of laterally disposed filter etc. means), and multiple detector elements in the two detectors that intercept the two separated beams, are present, respectively. It is further noted that as the two electromagnetic beams typically have a single spectroscopic source of electromagnetic radiation, source electromagnetic intensity drift and noise etc. show-up equally in real-time in baseline reference and sample system investigation signals, and that causes ratios of sample system investigation intensity, to the reference baseline intensity signals, at all wavelenghts, to be compensated therefore. However, as two Detectors are involved, (one to intercept the beam which interacts with a sample and one to intercept the beam that does not), it should be recognized that errors attributable to the Detectors, (eg. different calibration drifting characteristics), is not automatically compensated.
It should then be appreciated that while simultaneous use of two beams derived from a single spectroscopic source of electromagnetic radiation facilitates automatic compensation of changes in the output of said spectroscopic source of electromagnetic radiation, said approach also requires that two Detectors be utilized, and errors can develop based on changes in the two Detectors which do not necessarily exactly “track” one another. In comparison, it should also be appreciated that use of a single beam and single detector element to sequentially provide base-line and sample system investigation data, while avoiding the problems associated with the presence of two detectors, predisposes data acquired by use thereof to error caused by the requirement that electromagnetic radiation used to provide base-line and sample investigation data, while from the same source, must be accessed at different times, thus sorce output characteristic drift becomes a source of problems.
Continuing, typical practice, when investigating a sample system with a spectrophotometer using a single source beam and single detector, (dual beam in time), is to do baseline reference intensity data acquisition, wherein multiple wavelengths are dispersed, or perhaps separated by filtering etc., and monitored simultaneously by multiple detector elements, or wherein monochrometer is used to scan through a range of wavelengths and single detector element is utilized to sequentially monitor the results. A sample system is then entered into the single electromagnetic beam spectrophotometer system and corresponding intensity data is similarly acquired. Comparison of the baseline reference results to the corresponding sample system present data, on a wavelength by wavelength basis, allows forming desired ratio results.
It is generally noted that it is relatively easy to set a spectrophotometer system in a baseline reference configuration and do a monochrometer scan of wavelengths, then set the spectrophotometer in a sample system present configuration and do a similar monochrometer scan of wavelengths. The present inventors however, have noted that said just described monochrometer scanning practice is less than optimum as monochrometers have finite wavelength repeatable selection precisions associated therewith. For instance, what a monochrometer passes as a wavelength of “X” in the baseline scan is not necessarily repeatably precisely the same as the wavelength identified as “X” passed during the sample system investigation scan. This lack of repeatability is complicated where actual value accuracy errors in wavelength selection occur. In addition, as mentioned, electromagnetic radiation source intensity fluctuations can occur during one, (ie. baseline or sample system investigation), scan which are not similar to those in another scan. And, it is again mentioned that even where two beams derived from a single source are simultaneoulsy utilized, two detectors must be applied, and said characteritic output from each of said two detectors can drift differently with time, thereby entering error.
Ellipsometer, polarimeter or the like systems comprise a Source of Electromagnetic radiation, (preferebly scpectroscopic), a Polarizer, optionally a Compensator, a Stage for supporting a sample, optionally a Compensator, an Analyzer and a Detector. It is also possible to include a Monochromator to enable scanning through a range of wavelengths. Data which can be obtained with Ellipsometers, Polarimeter or the like systems are a ratio of intensities of, and a phase angle between, orthogonal components of a polarized beam of electromagentic radiation caused by interaction with a sample.
With the present invention in mind, a Search of Patents was conducted. Perhaps the most relevant Patent found was U.S. Pat. No. 4,832,491 to Sharpe et al. Said Patent describes a method of using electromagnetic radiation to investigate a sample system, involving using a monochrometer to set a wavelength, obtaining reference data, obtaining sample system data, forming a ratio of the sample system and reference data, and repeating said steps for additional wavelengths. Another Patent, U.S. Pat. No. 3,790,798 to Sternberg et al., describes a single beam system wherein reference data is obtained with filters in place in said system which pass wavelengths other than those which are absorbed by a sample analyte, (eg. gas in a sample containing cell). Said 798 Patent describes obtaining both sample and reference data and forming a ratio therebetween.
A Patent to Fukasawa et al., U.S. Pat. No. 4,577,106, describes a double beam spectrophotometer which contains means for allowing acquisition of dark, reference, sample and reference data, in that order.
A Patent to George, U.S. Pat. No. 3,986,776 describes baseline compensation in a dual beam spectrophotometer. During a calibration run a baseline error signal is generated, and said error signal is used to adjust a ratio of a sample to baseline signal during sample data acquisition.
U.S. Pat. No. 4,079,256 to Ford et al., describes a double-beam system in which two evaluations are combined to produce a derived reference signal in a situation wherein sample and reference signals do not occur at the same time, because a single spectrophotometer detector system it utilized.
U.S. Pat. Nos. 4,084,248 and 3,579,105 to Scott describe dual beam systems in which in the calibration run two beams are compared at each wavelength and adjustment disparities are calculated, said adjustments being applied during sample runs.
Patents found by the Examiner during Prosecution of the Parent application Ser. No. 09/862,881 are:                U.S. Pat. No. 5,991,022 to Buermann et al; and        U.S. Pat. No. 4,455,097 to Ichikawa et al.        
There are literally thousands of references available which focus on Ellipsometry, but none are known to teach partial replacement of spectroscopic data sets, hence none are identifed.
The focus of the presently disclosed invention is to teach partial substitution of data at specific wavelengths in a spectroscopic data set, said replaced data having been, by any means, determined to be suspect as to precision and/or accuracy.
Even in view of said prior art, need remains for, in the context of spectrophotometer and ellipsometer or the like systems, a methodology for improving the quality of data provided thereby.